Feature additions:
* It is possible to define a constant HTTP_CLIENT_QUIRK_MODE in your script,
if it is present then HTTP_Client will follow common browser behaviour
rather than RFC 2616. Currently this means: always do a GET request
on a 301 redirect (request #1854).
* HTTP_Client now analyzes the response body for <meta http-equiv="Refresh">
tags and follows the redirects defined in them (request #5734)
* Added possibility to send extra headers with requests (request #7552)
* It is now much easier to store permanent cookies received by HTTP_Client:
added magic __sleep() and __wakeup() methods to CookieManager class to aid
in its (un)serialization, added getCookieManager() method to HTTP_Client,
added possibility to pass CookieManager object to HTTP_Client's
constructor (request #7578).